Natural and synthetic proteins are becoming more and more important as drugs. When they are used for medical applications, their products must be sterilized. As means of sterilization, there are known heat sterilization in an autoclave, sterilization with ionizing radiation such as a γ ray or electron beam, gas sterilization with an ethylene oxide gas, plasma sterilization with hydrogen peroxide, and separate sterilization using a chemical sterilant comprising a glutaraldehyde formulation or a filter. However, the activities of proteins such as bioactive proteins are reduced by sterilization with heat or radiation. Sterilization with ethylene oxide has possibilities that a by-product may be produced by a chemical reaction and that a highly toxic residual gas may adversely affect the human body. Sterilization with a chemical sterilant has a problem that the resistance to a sterilant of a protein and changes in pH, ion intensity and temperature must be taken into consideration. Then, to manufacture pharmaceuticals and medical products containing or immobilizing a protein, their production processes must be entirely made in sterile conditions and a huge amount of production cost is required.
Although a solution containing a protein is subjected to separate sterilization with a filter, it is difficult to apply this separate sterilization to a composition containing large particles or a solid or semisolid composition.
EP0437095 teaches that a neutralized oxidized cellulose product combined with heparin or a heparin fragment (nORC) can be sterilized by gamma-ray irradiation. However, this document fails to teach the sterilization of ORC or n-ORC to which a protein is bound.
EP0562864 discloses a composite wound care substance containing a collagen sponge matrix, a second bioabsorbable polymer such as an oxidized regenerated cellulose (ORC) dispersed fiber and an active agent such as peptide. This document teaches that the active agent may be contained in the matrix, the bioabsorbable polymer or both of them and that the composite sponge substance can be sterilized while it is packaged.
U.S. Pat. No. 5,730,933 discloses a method of sterilizing biologically active peptide with gamma-ray or electron-beam irradiation without the loss of the biological activity of the peptide. This method is a technology comprising the steps of forming a mixture of biologically active peptide and a foreign protein such as gelatin, freezing or lyophilizing this mixture, and irradiating it. This document teaches that the existence of the foreign protein stabilizes peptide and prevents the reduction of the activity of peptide.
WO2000/033893 discloses a complex of therapeutic peptide and a polysaccharide selected from the group consisting of oxidized regenerated cellulose, neutralized oxidized regenerated cellulose and mixtures thereof. This document teaches that when peptide is formulated together with an effective amount of the polysaccharide before sterilization with ionizing radiation, the biological activity of the peptide therapeutic agent is not lost and is stabilized if peptide is sterilized with ionizing radiation.
However, these documents do not suggest that the structural change such as aggregation and deactivation of a protein which occur during sterilization with ionizing radiation can be suppressed by an aliphatic polyester.
Meanwhile, JP-A 2011-47089 discloses a process for producing an enzyme-containing nanofiber having excellent enzyme activity. In this process, a spinning solution containing an enzyme and a polymer dissolved in a nonaqueous solvent is spun by an electrostatic spinning method to form a zymogen nanofiber which is then imparted with water and dried. However, this document is silent about the sterilization of the enzyme-containing nanofiber.